This invention relates to Uninterruptable Power Supplies (UPS), and more specifically, to the class of UPS used to provide power to an Internet Telephone (IT), an Internet Telephone Cable Modem (ITCM), and an Internet Telephone xDSL Modem (ITDM).
This invention is in the field of power sources which power a load such as an internet telephone, wherein the power source includes both an internal source such as a rechargeable battery, and an external source such as mains voltage. In an internet telephone, power is usually furnished to the telephone through the mains. However, during power outages, it is critical that the telephone operate reliably using the internal source. Moreover, since mains power failures are infrequent, it is very important that the reserve capacity of the internal source be known in advance of switching over to this source during a time of power outage. It is also important to advise the user to replace the battery when it demonstrates insufficient reserve capacity, rather than make this determination when there is no alternative power source available.
It is desired to periodically measure the reserve capacity of the battery as accurately as possible to ascertain that it is capable of operating the internet telephone in the event of mains power failure and to make such measurement when it is unlikely to interfere with a users utilization of the internet telephone.
There are several prior art techniques used to estimate the reserve charge in a battery. One class of system utilizes the open circuit voltage of the battery in comparison to the loaded voltage of the battery. One such example system is U.S. Pat. No. 4,180,770 by Eby. In this system, the difference between open circuit voltage and loaded voltage of the battery actuates a comparator which drives an indicator. Quite often, this load comprises a test load independent of the actual load, such that the test load provides for an accurate measurement. Another example system is described in U.S. Pat. No. 5,122,751 by Aita et al. In this patent, the test load comprises the actual device receiving power, and the reserve charge is determined by comparing the discharge curve for the present battery driving this actual load against a series of characteristic battery curves shown in FIG. 6 of this reference. When a match is made based on discharge characteristic, a depth of discharge is imputed to the battery. U.S. Pat. No. 5,650,712 by Kawai et al describes an algorithm whereby a circuit external to the battery monitors the charge added or subtracted from the battery, and stores this estimate in a memory. The reserve capacity is therefore indicated in this memory. U.S. Pat. No. 5,726,573 by Chen discloses an external power supply charging a battery. From time to time, a CPU requests a test of the battery, which only occurs when the battery has sufficient voltage. If the battery drops below a specified voltage during the test, a signal is sent to the CPU indicating this failure, and further tests are prevented until the battery is replaced.
The present invention comprises an AC/DC converter, a rechargeable battery, a device load typically comprising an internet telephone, a controller producing a BAT_TEST_L signal, and a multiplexer controlled by this BAT_TEST_L signal, whereby the internet telephone is either powered by the battery, or it is powered by the AC/DC converter through the external AC mains. Additionally, there is a battery charging circuit, whereby the battery is charged by the AC/DC converter while the converter is powering the internet telephone. When external mains power source is present, the converter provides a trickle charge to the battery, typically at a rate which would require 24 hours to fully charge the battery from a discharged initial state. During the duration of trickle charge, the battery reaches a fully charged state. When the controller determines that it is time to test the reserve capacity of the battery, it asserts a BAT_TEST_L signal, which causes the multiplexer to change the power source to the battery. During this time, the battery charging circuit is disabled. For the duration of measurement, the battery is furnishing current to the internet telephone, which acts as a live test load, and the output voltage and current of the battery are measured. After the measurement interval has ended, the controller deasserts the BAT_TEST_L signal, and the internet telephone is again powered by the converter through the external AC mains. From the acquired data during the measurement interval, a discharge time Td and a discharge voltage Vd is extracted. The Td and Vd values are compared to an exemplar set of values stored in the controller, and a value for reserve capacity is determined. This reserve capacity value is stored in the non-volatile random access memory (NVRAM) of the controller. The example set of values related to the reserve capacity of the battery is pre-determined at the factory, and a minimum reserve capacity value can be chosen for a particular class of battery. If the value of reserve capacity measured during the battery test falls below a minimum reserve capacity value, a message is sent to the user requesting replacement of the battery. The time that the charge estimation test is initiated and the interval between such tests is varied according to the known state of the battery and the usage pattern of the telephone. Tests are always initiated during times of minimum use, based on usage patterns measured by the network to which the IT is attached. The frequency of the battery reserve capacity test is varied according to the state of the battery. For example, a new battery is tested less frequently than a battery with a diminishing reserve capacity margin over acceptable thresholds.
In addition to the measurement of Td and Vd values, each time the battery is discharged by the IT during a mains power fail condition, a record is kept in the non-volatile memory (NVRAM) of the controller of the number of discharges and depth of each discharge. Since the battery life may also be estimated by the depth of discharge and the number of such discharges, it is also possible to estimate the life of the battery based on these discharge records. When the threshold for discharges at various depths is exceeded, a message is sent to replace the battery.
The reserve capacity threshold and the discharge depth and discharge cycle threshold of the battery can be updated after the internet telephone has been installed in the field, through the network connection between the internet telephone and the Service Provider (the Central Office). This capability to revise the various threshold values after installation allows the Service Provider to obtain the maximum usage from a battery. Additionally, the discharge record and the current reserve capacity of the battery can also be retrieved by the Service Provider periodically. This capability allows the Service Provider to plan replacement battery procurement in an orderly fashion.
A first object of the invention is to enable the measurement of reserve capacity of a battery using the most accurate load possible. A second object of the invention is to vary the interval between tests according to measured parameters and the current internet telephone operating state, in order not to interrupt the normal operations of the internet telephone. A third object of the invention is to disable reserve capacity measurement when an excessively low reserve capacity measurement has been made, or it has been detected that the previous reserve capacity measurement test failed to complete. A fourth object of the invention is to allow the alteration of battery replacement criteria after the UPS has been deployed through network updates to gain maximum useful life from the battery, and to allow the monitoring of reserve capacity of all batteries deployed in the field.